Device with a drum for coating material which rotates about an axis, in particular for film and/or sugar-coating, the drum having an inner space which may be exposed to a fluid flow, wherein the inner space is associated with an element for guiding a gas flow which guides the gas flow as a controlled shell-shaped flow through the plane of the drum opening and, with at least one longitudinal component in the direction of the axis, through the inner space of the drum and wherein the element is formed by two cylindrical pipe sections which intermesh one another and delimit an annular gap between them.
A device of this type is known from EP-A-01 31 152.
In the case of the known device the drum rotates about an axis and the material to be coated inside the drum is exposed to a fluid flow. The fluid flow is guided via a distribution head at the end of the drum where the drive is provided into the inner space of the drum. Arms shaped like hollow bodies extend into the drum which comprise openings via which the fluid flow can be removed from the inner space of the drum.
Furthermore, a device for film or sugar-coating is known from the leaflet Hi-Coater WD 11.1982 SM/HICO-d 32.2000 under the term "Hi-Coater, the modern and economic system for the coating of tablets".
Devices of this kind are used in the pharmaceutical industry mainly for coating cores. The layers should be as uniform and smooth as possible and the revolving and rolling movements which cause the cores to be mixed with one another to a smaller or larger extent should be of such a nature that the wear, i.e. the shearing stress of the cores is kept small.
The sprayed cores should be dried as carefully as possible and the parameters specific to the method should be taken into consideration. The drying speed must be adjusted to the respective process in the best possible manner such that cracks in the coating of the core can be avoided for example.
In the case of the device known from the leaflet Hi-Coater WD 11.1982 SM/HICO-d 32.2000 the gas is guided to the drum in the area of the supply opening. The means by which the air is guided to the product bed are not very constructive. It immediately meets the surface of the supply opening opposite the air inlet opening. From there the incoming air moves towards the perforated pieces of sheet metal in the bottom area of the drum. Already in the inlet area the incoming air becomes turbulent and negative influences by a predetermined spray mist cannot be avoided. Furthermore the incoming air will preferably take the shortest way to the perforated pieces of sheet metal. This has the result that the heat and material exchange processes across the length of the drum are different.
In most cases, when the method steps are carried out one after the other or several at the same time, the drying process is the step during the entire method proceedings which determines the timing such that optimizing this is very advantageous. In addition thereto the drying process is also a method step in which the quality will be determined such that also from this point of view it is advisable to achieve that the cores are dried as uniformly as possible.
Considering the spraying device of the known device from WD 11.1982 SM/HICO-d 32.2000 it can be noted that the angle at which the spray jets are set with respect to the revolving product bed must be adjusted before a sugar-coating or film coating process can be started. Since the shape and the position of the cascade-like formation of cores that are carried upwards on the inside of the drum due to friction changes between the start of the process and a stationary state owing to mainly varying rotational speed of the drum, for optimizing the core treatment the setting angle of the spray jet with respect to the product bed would have to be changed also during the process.